It really depends on what you want. If you are going to use it exclusively with her mac, you can format it to mac extended journal if you want, but it isn't necessary. My back up drive is in this format, but only because I know it will never leave my Imac's side and I never use it for anything else. Remember, you won't be able to use the drive with a PC once you do this without reformatting it again. If you are going to be using the drive too, a partition might be handy, but again, it is not necessary.

lIíll keep it short and sweet ó Family. Religion. Friendship. These are the three demons you must slay if you wish to succeed in business. -Monty Burns